If you are trying to replace a glass fuse, you will most likely be able to visibly inspect the fuse to see if it's blown. If you see a breakage in the wire or a dark or metallic discoloration on the glass, the fuse is blown (shown below). However, if you are not able to tell if the fuse is blown by visual inspection, or if the fuse is ceramic and not transparent, you will need to test it.
If the fuse is blown, remove it. Be sure the power is off and no voltage is present. Fuse pullers make this step easy but if you don’t have one, grab screwdriver or pliers. Gently pry the fuse out by the ends. If the fuse tubing is glass, be careful to not crush the tubing.
You’ll want to find a replacement fuse identical to the original blown fuse. If you’re not sure which fuse to buy, check out our buying guide here. Once you have your replacement fuse, push one end into the clips. If your fuse has grooves on one end, be sure it's not upside down. Firmly push the other side in by pressing on the metal end. Don't apply pressure on the fragile tubing. If you can't push it in with your hand, grab a screwdriver or hammer and apply pressure onto the end of the fuse with the plastic handle. Once it's in, you can restore power.